Short Circuit Report

TB-254-357-005 Page No.1 of 12

FAULT LEVEL CALCULATIONS STUDY 1

INTRODUCTION NSPCL, A Joint Venture of NTPC and SAIL, is setting up an expansion of the Bhilai Power Project by 2x250 MW power generation at Bhilai, District Durg, Chhatisgarh. The installed capacity of existing Power Plants (Power Plant 1-PP1 and Power Plant 2- PP2) in Bhilai Steel Plant (BSP) is 110MW. The BSP load is 350 MW. In normal course, the Bhilai Power Project (Power Plant 3, PP3 consisting of G1 and G2) will work in parallel with Bhilai Steel Plant (BSP), existing Power Plants (PP1 and PP2) and PGCIL’s grid. PP3 will supply 240 MW to BSP. Around 40 MW are consumed by PP3 auxiliaries, the balance 220 MW will be exported to the grid at 400 kV. But during contingency conditions, there is a possibility of BSP together with PP1, PP2 and PP3 being islanded from grid. Under this islanding operation, PP3 shall be supplying power to Bhilai Steel Plant only through dedicated transmission lines connecting Bhilai Steel Plant to Bhilai Power Project. This report focuses on the development of a model of the electric power system in an expansion of the Bhilai Power Project by 2x250 MW power generation in order to perform short circuit study conducted on power system data as per TB-254-357-001- “Design Data, Load Flow and Island Mode of Operation Study” Report. The results of study serve to establish sequence data files to be used in further stability studies. SIMPOW, Power System Simulation Software is used for carrying out the Short Circuit studies.

2

Short Circuit Current Calculation A Short Circuit Study is critical for the safe, efficient, and economical operation of any electrical distribution system. A Short Circuit Study will help to ensure that personnel and equipment are protected by establishing proper short circuit current ratings. When an electrical fault exceeds the interrupting rating of the protective device, the consequences can be devastating, including injury, damaged electrical equipment, and costly downtime. Among the most important tasks, when planning and operating power systems, are the short-circuit current calculations (SCCs). Faults, i.e. short-circuits, can be minimized in the system through planning and design, and well-performed maintenance and operation of the system, but cannot be totally avoided. Protection settings and coordination and dimensioning of switchgear require accurate and detailed SCCs because switches and breakers have to be designed to switch off shortcircuits in a safe way and in short time. Short-circuits can cause mechanical oscillations in generators which can lead to oscillations in the power in the system, causing problems of stability in the power transfer. In the worst case this can lead to a blackout of the system. One last area to consider is that the installed equipment must be able to withstand the thermal and mechanical effects of short-circuit currents. Hence, it is very essential to conduct fault level calculation study for power system.

TB-254-357-005 Page No.2 of 12

3

Technical Requirements as per TS The maximum fundamental frequency short circuit current at the various 400 kV and 220 kV buses shall be limited to 40 kA for one second.

4

Input Data 1. Input data for the study is as per Report No: TB-254-357-001. 2. Single line diagram is taken to indicate the overall network around Bhilai Steel Plant for carrying out the short circuit studies.

5

Load Flow Cases The following load flow base cases [1] as described in Load Flow study were considered for calculating the Short Circuit levels. Case

CASE Name

Case Description

1

CASE 1

Parallel Operation of 2x250 MW PP3+PP2+PP1+BSP with Grid

2

CASE 2

Islanded Operation of 2x250 MW PP3+PP2+PP1+BSP no Grid

3

CASE 3

Islanded Operation of 1x250 MW PP3+PP2+PP1+BSP from Grid

No.

The power flow results for the above 3 cases are mentioned in Report No: TB-254-357-001.

6

Fault Studies The power system is divided into several different voltage levels, where calculations are made for short circuits on the 400 kV, 220kV and 132 kV levels. Three different cases are set up in order to evaluate the system, so that the maximum and minimum currents can be determined. Fault studies were carried out to determine fault levels under the below three cases. Fault Cases Case No.

CASE Name

1

CASE 1

2

CASE 2

3

CASE 3

TB-254-357-005 Page No.3 of 12

6.1

Base Cases Three phase to ground (3PSG) faults are applied at the following buses in cases 1 to 3.

S. No.

Bus Name

1

BESCL220

2

BESCL400

3

MSD5Ͳ220

4

MSD6Ͳ220

5

BP1TG1Ͳ6

6

BP1TG2Ͳ6

7

BP1TG0Ͳ6

8

MSD1Ͳ132

9

MSD2Ͳ132

10

MSD3Ͳ132

11

MSD4Ͳ132

12

MSD5Ͳ132

13

MSD6Ͳ132

14

M4SEC1Ͳ1

15

M4SEC2Ͳ1

16

M4SEC1Ͳ6

17

M4SEC2Ͳ6

18

M2DR1Ͳ6

19

M2DR2Ͳ6

20

M2VADͲ11

21

M2SMSͲ11

22

M2SEC1Ͳ1

TB-254-357-005 Page No.4 of 12 S. No.

Bus Name

23

M2SEC2Ͳ1

24

M2SEC1Ͳ6

25

M2SEC2Ͳ6

26

M2SEC3Ͳ6

27

M2SEC4Ͳ6

28

M6SEC1Ͳ1

29

M6SEC2Ͳ1

30

P2Ͳ1Ͳ132

31

P2Ͳ2Ͳ132

32

P2SEC1Ͳ6

33

P2SEC2Ͳ6

34

P2Ͳ21TͲ6

35

P2Ͳ22TͲ6

36

P2Ͳ23TͲ6

TB-254-357-005 Page No.5 of 12

7

MODELING & SIMULATION 7.1

Different cases

The different cases analyzed are a number of network configurations that are of interest to investigate. Three different cases are set up, where each case has a specific objective which is important to examine.

7.1.1

Case 1

Case 1 is set up at Parallel Operation of 2x250 MW PP3+PP2+PP1+BSP with Grid, with contribution from the 400 kV and 220kV grid and from the generators G1 and G1 respectively. PP3 generators are assumed to be operating at 1.05pu voltage in order to ensure the voltages in the study system within the limits. Both PP3 generators are supplying their rated power (250MW each). The short circuit current levels in the network are tabulated in Table.1. The short circuit current values obtained in the study system are within the limits, i.e. less than 40kA for one second. The 3 phase to ground and single phase to ground fault currents at each of the 400kV, 220kV and 132kV buses for case 1 are tabulated in Annexure A.

7.1.2

Case 2

Case 2 is set up at Islanded operation of 2X250 MW PP3, PP2, PP1 and BSP without grid connection. PP3 generators are assumed to be operating at 1.05pu voltage in order to ensure the voltages in the study system within the limits. Generator G1 is supplying 143 MW and generator G2 is supplying 142 MW to meet the reduced load requirement in the absence of export to grid. The short circuit current levels in the network are tabulated in Table.2. The short circuit current values obtained in the study system are within the limits, i.e. less than 40kA for one second. The 3 phase to ground and single phase to ground fault currents at each of the 400kV, 220kV and 132kV buses for case 2 are tabulated in Annexure B.

7.1.3

Case 3

Case 2 is set up at Islanded operation of 1X250 MW PP3, PP2, PP1 and BSP from grid connection. Only one PP3 generator (G1) is assumed to be operating at 1.03pu voltage and supplying 250 MW to BSP. The short circuit current levels in the network are tabulated in Table.2. The short circuit current values obtained in the study system are within the limits, i.e. less than 40kA for one second. The 3 phase to ground and single phase to ground fault currents at each of the 400kV, 220kV and 132kV buses for case 3 are tabulated in Annexure C.

.

TB-254-357-005 Page No.6 of 12

For each case, reported in Annexure A to C, the maximum fault current (fault KVA level) out of the fault currents on the selected 36 buses is shown in bold letters. Similarly, the minimum fault current (fault KVA level) out of the fault current on the selected 36 buses are shown in bold italics for each operating scenario.

8

Conclusions ƒ

The short circuit studies were conducted for the various base operating conditions and contingencies.

ƒ

Maximum fault currents were then determined at M2DR1-6 bus for case 1,BP1TG1-6 bus for case 2 and M2DR1-6 bus for case 3.

ƒ

The fault levels at various buses of 400kV, 220kV and 132kV were found to be lower than 40 kA as stipulated in Technical Specifications. Out of the reported fault levels, the minimum and maximum fault levels at the 400 kV, 220kV and 132kV buses in cases 1 to 3 are as shown below: CASE No.

ƒ

9

Minimum Fault Level

Maximum Fault Level

At Bus

Fault MVA

At Bus

Fault MVA

1

MSD6Ͳ132

2.424

BESCL220

10.287

2

MSD6Ͳ132

0.8466

BESCL400

1.4743

3

MSD4Ͳ132

0.03576

BESCL400

5.5377

The study summarises the results of short circuit levels under various conditions.

References: 1. TB-254-357-001- “Design Data, Load Flow and Island Mode of Operation Study” Report.

TB-254-357-005 Page No.7 of 12

Annexure A CASE 1

S.No.

Bus Name

1 PSG Fault

3 PSG Fault Short

Isc (kA)

Isc (kA)

circuit KVA

1

BESCL220

10.132

26.997

10287.24

2

BESCL400

4.685

12.998

9005.279

3

MSD5Ͳ220

9.817

26.278

10013.26

4

MSD6Ͳ220

9.803

26.317

10028.12

5

M3SEC1Ͳ1

0.365

21.827

434.7629

6

M3SEC2Ͳ1

0.337

28.71

571.8626

7

M3SEC3Ͳ1

0.376

28.711

571.8825

8

MSD1Ͳ132

4.047

10.366

2369.986

9

MSD2Ͳ132

5.385

13.175

3012.21

10

MSD3Ͳ132

4.75

12.206

2790.666

11

MSD4Ͳ132

3.307

9.059

2071.166

12

MSD5Ͳ132

0.587

14.247

3257.302

13

MSD6Ͳ132

1.788

10.604

2424.4

14

M4SEC1Ͳ1

0.081

13.26

264.1204

15

M4SEC2Ͳ1

0.081

13.26

264.1204

16

M4SEC1Ͳ6

0.145

8.523

97.43098

17

M4SEC2Ͳ6

0.145

8.52

97.39668

18

M2DR1Ͳ6

1.03

37.312

426.5334

19

M2DR2Ͳ6

1.171

37.179

425.0131

20

M2VADͲ11

0.816

7.367

146.7402

TB-254-357-005 Page No.8 of 12 21

M2SMSͲ11

2.04

13.918

277.2269

22

M2SEC1Ͳ1

0.143

23.05

459.1234

23

M2SEC2Ͳ1

0.143

23.05

459.1234

24

M2SEC1Ͳ6

1.03

37.131

424.4643

25

M2SEC2Ͳ6

1.034

37.124

424.3843

26

M2SEC3Ͳ6

1.03

37.159

424.7844

27

M2SEC4Ͳ6

1.017

37.151

424.693

28

M6SEC1Ͳ1

0.682

13.809

275.0557

29

M6SEC2Ͳ1

0.682

13.809

275.0557

30

P2Ͳ1Ͳ132

4.765

12.383

2831.134

31

P2Ͳ2Ͳ132

2.932

8.576

1960.737

32

P2SEC1Ͳ6

4.067

12.163

139.0418

33

P2SEC2Ͳ6

4.07

12.162

139.0303

34

P2Ͳ21TͲ6

1.138

3.416

39.05012

35

P2Ͳ22TͲ6

1.138

3.416

39.05012

36

P2Ͳ23TͲ6

1.125

3.347

38.26135

TB-254-357-005 Page No.9 of 12

Annexure B CASE 2

S.No.

Bus Name

1 PSG Fault

3 PSG Fault Short

Isc (kA)

Isc (kA)

circuit KVA

1

BESCL220

0.089

3.388

1291.001

2

BESCL400

0.745

2.128

1474.322

3

MSD5Ͳ220

0.016

3.377

1286.81

4

MSD6Ͳ220

0.751

3.382

1288.715

5

BP1TG1Ͳ6

4.018

30.076

343.8149

6

BP1TG2Ͳ6

3.779

30.074

343.792

7

BP1TG0Ͳ6

4.365

24.876

284.3709

8

MSD1Ͳ132

0.422

4.408

1007.804

9

MSD2Ͳ132

1.455

4.772

1091.026

10

MSD3Ͳ132

0.03

4.586

1048.5

11

MSD4Ͳ132

0.82

4.091

935.3282

12

MSD5Ͳ132

0.809

4.22

964.8216

13

MSD6Ͳ132

0.557

3.703

846.6195

14

M4SEC1Ͳ1

1.779

10.483

208.8065

15

M4SEC2Ͳ1

1.78

10.483

208.8065

16

M4SEC1Ͳ6

0.007

7.532

86.10232

17

M4SEC2Ͳ6

0.005

7.529

86.06803

18

M2DR1Ͳ6

0.683

26.374

301.4953

19

M2DR2Ͳ6

0.681

26.302

300.6722

20

M2VADͲ11

0.939

6.3

125.4871

TB-254-357-005 Page No.10 of 12 21

M2SMSͲ11

1.877

11.066

220.4191

22

M2SEC1Ͳ1

0.191

16.168

322.0437

23

M2SEC2Ͳ1

0.215

16.168

322.0437

24

M2SEC1Ͳ6

0.146

26.274

300.3522

25

M2SEC2Ͳ6

0.126

26.269

300.295

26

M2SEC3Ͳ6

0.401

26.291

300.5465

27

M2SEC4Ͳ6

0.117

26.287

300.5008

28

M6SEC1Ͳ1

1.528

10.307

205.3008

29

M6SEC2Ͳ1

1.528

10.307

205.3008

30

P2Ͳ1Ͳ132

1.71

4.658

1064.962

31

P2Ͳ2Ͳ132

1.376

4.034

922.2963

32

P2SEC1Ͳ6

1.945

10.602

121.1971

33

P2SEC2Ͳ6

1.947

10.6

121.1743

34

P2Ͳ21TͲ6

0.506

3.181

36.36371

35

P2Ͳ22TͲ6

0.506

3.181

36.36371

36

P2Ͳ23TͲ6

0.551

3.131

35.79214

TB-254-357-005 Page No.11 of 12

Annexure C CASE 3

S.No.

Bus Name

1 PSG Fault

3 PSG Fault Short

Isc (kA)

Isc (kA)

circuit KVA

1

BESCL220

0.143

8.316

3168.822

2

BESCL400

2.117

7.993

5537.713

3

MSD5Ͳ220

0.004

8.249

3143.291

4

MSD6Ͳ220

1.053

8.256

3145.959

5

BP1TG1Ͳ6

3.59

28.622

327.1934

6

BP1TG2Ͳ6

3.535

28.62

327.1705

7

BP1TG0Ͳ6

3.943

23.811

272.1963

8

MSD1Ͳ132

0.423

6.802

1555.146

9

MSD2Ͳ132

1.955

7.916

1809.841

10

MSD3Ͳ132

0.044

7.534

1722.504

11

MSD4Ͳ132

1.107

6.206

1418.882

12

MSD5Ͳ132

1.544

8.33

1904.494

13

MSD6Ͳ132

1.039

6.945

1587.84

14

M4SEC1Ͳ1

2.271

12.486

248.7034

15

M4SEC2Ͳ1

2.273

12.486

248.7034

16

M4SEC1Ͳ6

0.01

8.332

95.24755

17

M4SEC2Ͳ6

0.007

8.328

95.20183

18

M2DR1Ͳ6

0.992

33.899

387.5176

19

M2DR2Ͳ6

0.974

33.79

386.2716

20

M2VADͲ11

1.152

7.145

142.3183

TB-254-357-005 Page No.12 of 12 21

M2SMSͲ11

2.266

13.051

259.9574

22

M2SEC1Ͳ1

0.275

20.875

415.8004

23

M2SEC2Ͳ1

0.318

20.875

415.8004

24

M2SEC1Ͳ6

0.215

33.75

385.8143

25

M2SEC2Ͳ6

0.192

33.743

385.7343

26

M2SEC3Ͳ6

0.116

33.743

385.7343

27

M2SEC4Ͳ6

0.186

33.743

385.7343

28

M6SEC1Ͳ1

2.445

13.116

261.2522

29

M6SEC2Ͳ1

2.445

13.116

261.2522

30

P2Ͳ1Ͳ132

2.457

7.614

1740.794

31

P2Ͳ2Ͳ132

1.83

5.939

1357.838

32

P2SEC1Ͳ6

1.968

10.826

123.7578

33

P2SEC2Ͳ6

1.971

10.824

123.7349

34

P2Ͳ21TͲ6

0.512

3.204

36.62664

35

P2Ͳ22TͲ6

0.512

3.204

36.62664

36

P2Ͳ23TͲ6

0.547

3.129

35.76927